Abstract
In high-intensity interval training the interval duration can be adjusted to optimize training results in oxygen uptake, cardiac output, and local oxygen supply. This study aimed to compare these variables in two interval trainings (long intervals HIIT3m: 3 min work, 3 min active rest vs. short intervals HIIT30s: 30 s work, 30 s active rest) at the same overall work rate and training duration. 24 participants accomplished both protocols, (work: 80% power output at VO2peak, relief: 85% power output at gas exchange threshold) in randomized order. Spirometry, impedance cardiography, and near-infrared spectroscopy were used to analyze the physiological stress of the cardiopulmonary system and muscle tissue. Although times above gas exchange threshold were shorter in HIIT3m (HIIT3m 1669.9 ± 310.9 s vs. HIIT30s 1769.5 ± 189.0 s, p = 0.034), both protocols evoked similar average fractional utilization of VO2peak (HIIT3m 65.23 ± 4.68% VO2peak vs. HIIT30s 64.39 ± 6.78% VO2peak, p = 0.261). However, HIIT3m resulted in higher cardiovascular responses during the loaded phases (VO2 p < 0.001, cardiac output p < 0.001). Local hemodynamics were not different between both protocols. Average physiological responses were not different in both protocols owning to incomplete rests in HIIT30s and large response amplitudes in HIIT3m. Despite lower acute cardiovascular stress in HIIT30s, short submaximal intervals may also trigger microvascular and metabolic adaptions similar to HIIT3m. Therefore, the adaption of interval duration is an important tool to adjust the goals of interval training to the needs of the athlete or patient.
Highlights
Interval training is an often-used training modality to improve endurance performance in athletes and cardiorespiratory fitness in patients [1–3]
We hypothesized that long interval duration, i.e., 3 min work, has higher cardiometabolic demand compared to short interval duration, i.e., 30 s, at same overall work
There was no significant difference in average oxygen uptake in any of the five sections between both protocols, there was a significant interaction effect between the first and second as well as the fourth and fifth section (ANOVA p ≤ 0.001, post hoc tests p ≤ 0.002)
Summary
Interval training is an often-used training modality to improve endurance performance in athletes and cardiorespiratory fitness in patients [1–3]. Buchheit & Laursen [1] defined multiple exercise variables used in the design of an interval exercise session including intensities and durations of work and relief phases, the work modality, and the combination of exercise series The manipulation of these factors adjusts the interval training in order to meet the demands of the sport, the athlete’s profile, or the patient’s possibilities [1]. Due to intermittent exercise of work and relief, HIIT achieves longer times at high rates of oxygen uptake (VO2 ) compared to long slow distance or moderate continuous training with the same training duration [1,5]. Our study aimed to compare two interval regimens of equal overall work rate but the different composition of workand relief-interval duration in respect of local and central cardiovascular effects. Despite the different cardiometabolic demands, both interval protocols achieve similar effects in acute microvascular oxygen distribution
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